The goal is to study human leukemias and non-Hodgkin's lymphomas using a multidisciplinary approach encompassing morphology, immunologic markers, cytogenetics, and flow microfluorometric analysis of DNA content, cell size, and cell kinetics in order to improve characterization and classification of these diseases. Cell suspensions and frozen tissues from more than 731 cases of non-Hodgkin's lymphomas, lymphocytic leukemias, and reactive lymphoproliferative conditions have been studied during the past year. Representative studies completed include: (1)\Twenty-one cases of lymphoblastic lymphoma were studied using a panel of monoclonal antibodies. Fifteen cases had a T-cell immunologic phenotype, two showed a "pre-B-cell" phenotype frequently found in acute lymphoblastic leukemias (BA-1 and BA-2 positive), one showed strong reactivity with the Leu-7 and Leu-11 antibodies, and one case showed monoclonal surface membrane immunoglobulin production characterized by kappa light and IgM heavy chains. (2)\To evaluate transport medium (Michel's) and its effect on preserving the antigenicity of lymphocyte surface markers for immunologic evaluation, a comparative study of 55 consecutive cases of a variety of malignant lymphomas and benign lymphoid disorders was completed. Our study indicates that the morphologic and immunologic results obtained by cryostat fresh-frozen section technique are superior to those obtained from the study of frozen sections previously maintained in transport media, a finding especially applicable for the study of monoclonality in B-cell lymphoproliferative disorders. (3)\We have described three cases of follicular lymphomas in which the follicular center cells exhibited pronounced nuclear irregularities with numerous cells having convoluted and cerebriform shapes. While the architectural pattern suggested B-cell lymphoma, the cytologic features suggested that the neoplastic lymphocytes were of the T-cell type. Immunologic studies (on frozen sections by the immunoperoxidase technique in all three cases and cell suspension studies in two cases) showed that the follicular center cells were clearly monoclonal B cells. The results of our studies suggest that architectural pattern (follicular) is a more reliable predictor of immunologic phenotype than cytologic features. (4)